Why?
First and most importantly, because it's accurate.
But nearly as important is the recognition that a huge part of the Spanish speaking community is more interested in Spanish speaking dictators than ones who speak Russian, Hungarian or even German.
And the GOP knows this! The GOP has successfully convinced a lot of people that *the Democrats* are the ones like Castro and Chavez. Many people here lived nightmares under these men and the GOP constantly tells them the Democrats are them.